Pronounced Surface Sensitivity of Hydroxylamine Oxidation on Gold Single-Crystal Electrodes in Acidic and Neutral Aqueous Solutions

The oxidation of hydroxylamine on the three low index faces of Au single crystal has been investigated by cyclic voltammetry in buffered aqueous solutions in the pH range 1-7 under quiescent conditions. The results obtained have shown that the onset potential for the reaction on Au(100) is more negative, and the current in the region of small overpotentials is higher than for Au(110) and Au(111) regardless of the pH of the solution. Measurements performed in phosphate buffer (pH 7) with single crystal rotating disk electrodes in the hanging meniscus configuration yielded rather linear Tafel slopes in the small overpotential region for Au(111) and Au(110), which were higher than those found for Au(100). This affords clear evidence that the mechanism for this latter surface is different that for the other two faces involving in all likelihood one or more yet to be identified adsorbed intermediates.